Intro to Climate Science
Table of Contents
Unit 3 Overview: Radiation and Earth's Energy Balance
3.1 Solar radiation and Earth's energy budget
3.2 Greenhouse effect and radiative forcing
3.3 Albedo and its impact on climate
3.4 Heat transfer mechanisms in the Earth system

The greenhouse effect, a natural process that warms Earth's surface, is crucial for maintaining habitable temperatures. Without it, our planet would be a frigid -18°C. However, human activities have amplified this effect, leading to global warming and climate change.

Greenhouse gases like CO2, methane, and water vapor trap heat in the atmosphere. Their concentrations have increased due to fossil fuel burning, deforestation, and agriculture. This has caused Earth's average temperature to rise by 1.1°C since pre-industrial times, with more warming projected unless emissions are reduced.

The Greenhouse Effect and Earth's Temperature

Greenhouse effect and Earth's temperature

  • Natural process warms Earth's surface and lower atmosphere
    • Greenhouse gases in atmosphere absorb and re-emit infrared radiation emitted by Earth's surface trapping heat in lower atmosphere and warming planet (CO2, methane, water vapor)
  • Without greenhouse effect, Earth's average surface temperature would be about -18°C (0°F)
    • Greenhouse effect maintains Earth's current average surface temperature around 15°C (59°F) making it habitable for life as we know it
  • Enhanced greenhouse effect amplifies natural greenhouse effect leading to additional warming
    • Human activities have increased greenhouse gas concentrations in atmosphere (burning fossil fuels, deforestation)

Main greenhouse gases and sources

  • Carbon dioxide (CO2)
    • Burning fossil fuels (coal, oil, natural gas) releases CO2 into atmosphere
    • Deforestation and land-use changes reduce natural carbon sinks and contribute to CO2 emissions
    • Cement production involves calcination of limestone, releasing CO2 as a byproduct
  • Methane (CH4)
    • Agriculture (livestock digestion, rice cultivation in flooded fields) produces methane emissions
    • Landfills and waste management facilities generate methane as organic waste decomposes anaerobically
    • Fossil fuel production and distribution can leak methane during extraction, processing, and transport (natural gas, oil)
  • Nitrous oxide (N2O)
    • Agricultural practices (nitrogen-based fertilizer use, soil management) stimulate N2O production by soil bacteria
    • Industrial processes (nylon production, nitric acid production) release N2O as a byproduct
    • Biomass burning (wildfires, agricultural waste burning) emits N2O among other pollutants
  • Water vapor (H2O)
    • Evaporation from oceans, lakes, and rivers adds water vapor to atmosphere
    • Transpiration from plants releases water vapor during photosynthesis
    • Atmospheric water vapor concentrations increase in response to warming caused by other greenhouse gases (feedback loop)
  • Ozone (O3) in lower atmosphere
    • Photochemical reactions involving nitrogen oxides and volatile organic compounds form ozone near Earth's surface
    • Ozone acts as a secondary greenhouse gas in the troposphere (ground-level ozone)

Radiative Forcing and Climate Change

Radiative forcing in climate systems

  • Radiative forcing is change in net irradiance (downward minus upward) at tropopause due to change in external driver of climate change
    • Measured in watts per square meter (W/m²) quantifying energy imbalance
    • Positive radiative forcing leads to warming, while negative radiative forcing leads to cooling (energy input vs output)
  • Greenhouse gases impose positive radiative forcing
    • Absorb and re-emit more infrared radiation back to Earth's surface enhancing greenhouse effect
  • Other factors contribute to radiative forcing
    • Changes in solar irradiance (variations in sun's energy output)
    • Volcanic eruptions exert short-term negative forcing due to reflective aerosols injected into stratosphere
    • Land-use changes alter surface albedo (reflectivity) affecting energy balance
  • Radiative forcing quantifies and compares influence of different factors on Earth's energy balance and temperature
    • Anthropogenic factors (greenhouse gases, aerosols, land-use changes) dominate recent forcing trends

Greenhouse gases vs global temperatures

  • Higher greenhouse gas concentrations lead to increased radiative forcing and warming
    • Atmospheric CO2 concentrations have increased from pre-industrial levels of ~280 ppm to over 410 ppm today primarily due to human activities (burning fossil fuels, land-use changes)
    • Methane, nitrous oxide, and other greenhouse gas concentrations have also risen significantly since pre-industrial times
  • Earth's average surface temperature has risen by approximately 1.1°C since pre-industrial era
    • Rate of warming has accelerated in recent decades with warmest years on record all occurring since 2000 (2016, 2020, 2019)
    • Warming is not uniform across globe (higher latitudes and land areas warm faster than global average)
  • Climate models project further warming as greenhouse gas concentrations continue to rise
    • Amount of future warming depends on rate and magnitude of greenhouse gas emissions (different emission scenarios)
    • Limiting warming to 1.5°C or 2°C above pre-industrial levels requires significant reductions in emissions to reach net-zero by mid-to-late century
    • Continued high emissions lead to more severe and irreversible impacts (sea level rise, ecosystem shifts, extreme weather events)

Key Terms to Review (25)

Thermal radiation: Thermal radiation is the emission of electromagnetic radiation from the surface of an object due to its temperature. This form of radiation is a key process in transferring heat energy and plays a vital role in the Earth's energy balance, especially concerning how energy is absorbed and emitted within the atmosphere and by the Earth's surface.
Energy balance: Energy balance refers to the equilibrium between the amount of energy Earth receives from the Sun and the amount of energy that is radiated back into space. This balance is crucial for maintaining stable climate conditions, as any imbalance can lead to changes in temperature and climate systems. It involves understanding how different processes, such as the greenhouse effect and radiative forcing, influence the distribution and movement of energy within Earth's atmosphere and surface.
Energy budget: The energy budget refers to the balance between the incoming energy from the sun and the outgoing energy that Earth radiates back into space. This balance is crucial for maintaining the planet's climate and temperature, influencing various processes such as weather patterns, ocean currents, and ecological systems. Understanding this concept helps to grasp how changes in energy absorption and emission, driven by factors like albedo and greenhouse gases, affect global warming and climate change.
Albedo Effect: The albedo effect refers to the measure of reflectivity of a surface, specifically how much sunlight is reflected back into space without being absorbed. This effect plays a critical role in Earth's energy balance and climate by influencing temperature regulation and contributing to variations in climate patterns based on surface types, such as ice, water, and vegetation.
Feedback loop: A feedback loop is a process where the output of a system influences its own input, creating a cyclical effect that can amplify or dampen changes within the system. In climate science, feedback loops are crucial in understanding how changes in the environment can lead to further alterations, especially concerning radiative forcing and the greenhouse effect, impacting global temperatures and climate patterns.
Water vapor: Water vapor is the gaseous state of water that exists in the atmosphere and plays a crucial role in Earth's climate system. It is a significant greenhouse gas, contributing to the greenhouse effect by trapping heat in the atmosphere and influencing weather patterns and precipitation. Its presence also affects other climate drivers and radiative forcing, making it an essential component of climate science.
Nitrous oxide: Nitrous oxide (N₂O) is a potent greenhouse gas that significantly contributes to climate change. It has a much higher global warming potential compared to carbon dioxide, making it a critical focus in discussions about greenhouse gases and their sources. The interactions of nitrous oxide within the atmosphere play a crucial role in radiative forcing and the overall energy balance of the Earth.
Carbon dioxide: Carbon dioxide (CO₂) is a colorless, odorless gas that is naturally present in Earth's atmosphere as a result of volcanic eruptions, respiration, and the decomposition of organic matter. It plays a critical role in the greenhouse effect and is a major contributor to global warming due to its ability to trap heat in the atmosphere.
Methane: Methane is a potent greenhouse gas that is a significant contributor to climate change, with a global warming potential much higher than carbon dioxide over a short time frame. Its role in the atmosphere includes contributing to radiative forcing, trapping heat and influencing Earth's energy balance. Understanding methane's sources and trends is critical for addressing its impact on climate change and global warming.
Negative radiative forcing: Negative radiative forcing refers to a process that causes a net cooling effect on the Earth's climate system by reducing the amount of energy absorbed by the atmosphere. It occurs when certain factors, such as increased reflectivity due to aerosols or changes in land use, lead to less solar radiation being absorbed. This concept is essential in understanding the balance of energy in the climate system and how various components can either contribute to warming or cooling effects.
Positive radiative forcing: Positive radiative forcing refers to the net increase in energy absorbed by the Earth's atmosphere due to greenhouse gases and other climate factors, leading to warming. This imbalance in the Earth's energy budget is crucial for understanding how certain substances can contribute to global temperature rise, ultimately influencing climate change and the greenhouse effect.
Kyoto Protocol: The Kyoto Protocol is an international treaty that commits its parties to reduce greenhouse gas emissions, based on the premise that global warming exists and human-made CO2 emissions have caused it. This agreement reflects the growing acknowledgment of climate change and aims to set legally binding obligations for developed countries to decrease their emissions, thus connecting to broader discussions about climate science, global temperature trends, and greenhouse gas management.
Global warming: Global warming refers to the long-term increase in Earth's average surface temperature due to human activities, primarily the burning of fossil fuels, which increases concentrations of greenhouse gases in the atmosphere. This rise in temperature impacts climate patterns, causing changes in weather systems, rising sea levels, and disruptions in ecosystems.
Radiative forcing: Radiative forcing is a measure of the influence a factor has on the energy balance of the Earth's atmosphere, usually expressed in watts per square meter (W/m²). It quantifies how different factors, such as greenhouse gases or aerosols, affect the balance of incoming solar energy and outgoing infrared radiation, thus playing a critical role in climate change dynamics.
Climate sensitivity: Climate sensitivity is a measure of how much the Earth's average temperature will increase in response to a doubling of atmospheric carbon dioxide (CO2) concentrations. It is a crucial concept in understanding the potential impacts of climate change, as it helps estimate future temperature changes based on current and projected levels of greenhouse gases, radiative forcing, and various climate feedback mechanisms.
Negative feedback: Negative feedback is a process where the output of a system reduces or dampens the initial stimulus, helping to maintain equilibrium within that system. In climate science, negative feedback mechanisms can stabilize the climate system by counteracting changes, such as temperature fluctuations or alterations in carbon levels, ensuring that the Earth remains in balance despite various perturbations.
Positive Feedback: Positive feedback refers to a process where an initial change in a system leads to further changes that amplify the original effect, creating a cycle of increasing impact. This concept is crucial in understanding various environmental and climate processes, as it can lead to significant and often rapid changes in conditions, sometimes exacerbating the initial issue.
Greenhouse effect: The greenhouse effect is a natural process where certain gases in the Earth's atmosphere trap heat, preventing it from escaping back into space and thereby warming the planet. This effect is crucial for maintaining a habitable climate, as it helps regulate temperatures and supports life on Earth. However, human activities have intensified this effect by increasing the concentration of greenhouse gases, leading to global warming and climate change.
Climate change: Climate change refers to significant and lasting changes in the Earth's climate, particularly a rise in global temperatures due to increased concentrations of greenhouse gases in the atmosphere. This phenomenon affects various aspects of the environment, including weather patterns, ecosystems, and human health, leading to widespread impacts on the planet.
Radiative equilibrium: Radiative equilibrium refers to the state in which the energy absorbed by an object, such as the Earth, is equal to the energy it emits back into space. This balance is crucial in maintaining a stable climate, as any imbalance can lead to temperature changes and alterations in weather patterns. Achieving radiative equilibrium is fundamental in understanding how the greenhouse effect and radiative forcing influence the Earth's energy budget and climate system.
Watts per square meter: Watts per square meter is a unit of measurement used to quantify the amount of power received or emitted by a surface area of one square meter. This term is crucial for understanding how energy is transferred in the context of solar radiation, Earth's energy budget, and the greenhouse effect. It helps illustrate the efficiency of energy absorption, the impact of greenhouse gases, and how changes in energy balance can influence global temperatures.
Parts per million: Parts per million (ppm) is a unit of measurement that expresses the concentration of a substance in relation to one million parts of a solution or mixture. It is commonly used to quantify the levels of gases in the atmosphere, particularly greenhouse gases, and helps illustrate their potential impact on climate change through the greenhouse effect and radiative forcing.
Paris Agreement: The Paris Agreement is a landmark international treaty adopted in 2015 that aims to address climate change by limiting global warming to well below 2 degrees Celsius above pre-industrial levels, while pursuing efforts to limit the temperature increase to 1.5 degrees Celsius. It establishes a framework for countries to set and achieve their own greenhouse gas reduction targets, emphasizing the importance of sustainable development and climate resilience.
Atmospheric insulation: Atmospheric insulation refers to the ability of the Earth's atmosphere to trap heat and maintain temperatures suitable for life. This process is largely facilitated by greenhouse gases, which absorb and re-emit infrared radiation, creating a warming effect known as the greenhouse effect. This natural insulation plays a crucial role in regulating the Earth's climate by preventing heat from escaping into space, thus maintaining a stable environment for ecosystems and human activities.
Ozone: Ozone is a molecule composed of three oxygen atoms, typically found in two distinct regions of the Earth's atmosphere: the stratosphere and the troposphere. In the stratosphere, ozone forms the ozone layer, which protects living organisms from harmful ultraviolet (UV) radiation. In contrast, at ground level in the troposphere, ozone can act as a harmful air pollutant and a greenhouse gas, contributing to climate change and various health issues.